The transponder [on Flight 77] went off about 9 a.m., the company said.

At that moment, the flight would have been under the control of the Indianapolis Air Route Traffic Control Center, one of 20 regional centers that track flights between airports.

The trouble should have been instantly noticeable, traffic controllers say.

Flight 77, like other planes, at first showed up on radar screens as a short solid line, with a readout that identifies the plane and gives its altitude and speed. When the transponder shuts down, the short line vanishes. The speed number goes away, too.

"It's just something that catches your eye,'' one controller says.

And it's not that unusual. Transponders fail from time to time; commercial aircraft are required to carry a spare. Although it isn't clear what happened in the case of Flight 77, a controller's first move typically would be to contact the pilot, and tell them the transponder wasn't working.

As former air traffic controller Robin Hordon, who knows the flight corridor which the two planes which hit the Twin Towers flew "like the back of my hand" and who handled two actual hijackings says:

It is important for people to understand that scrambling jet fighters to intercept aircraft showing the signs of experiencing “IN-FLIGHT EMERGENCIES” such as going off course without authorization,losing a transponder signal and/or losing radio contact is a common and routine taskexecuted jointly between the FAA and NORAD controllers. The entire “national defense-first responder” intercept system has many highly-trained civilian and military personnel who are committed and well-trained to this task. FAA and NORAD continuously monitor our skies and fighter planes and pilots are on the ready 24/7 to handle these situations. Jet fighters typically intercept any suspect plane over the United States within 10 - 15 minutes of notification of a problem.

This type of "immediate, high speed, high priority and emergency" scramble had been happening regularly approximately 75 - 150 times per year for ten years. In the same ten years, there were ZERO "low speed, delayed reaction, and low priority" hijacking scrambles reported, which means that the only time interceptors were ever scrambled for ten years before 9/11, they were using the high speed immediate scrambles.

On 9/11, Flight 77 was in fact tracked on radar, and could have been intercepted with fighter jets. However, the plane was allowed to go on a joy-ride all over the country with its transponder off for three-quarters of an hour. As the above-quoted Miami-Herald article states:

Forty-five minutes. That's how long American Airlines Flight 77 meandered through the air headed for the White House, its flight plan abandoned, its radar beacon silent.

* * *

Who was watching in those 45 minutes?

"That's a question that more and more people are going to ask,'' said one controller in Miami. "What the hell went on here? Was anyone doing anything about it? Just as a national defense thing, how are they able to fly around and no one go after them?''

Even with the transponder silent, the plane should have been visible on radar, both to controllers who handle cross-continent air traffic and to a Federal Aviation Administration command center outside of Washington, according to air traffic controllers.

The FAA, which handles air traffic control, would not discuss the track of Flight 77 or what happened in air-control centers while it was in flight. Neither would American Airlines.

***

But even if the plane remained silent, controllers could still find it -- by switching their screen display to the old-fashioned radar that bounces a signal off the plane's metal skin.

***

Military jets are routinely scrambled in the case of hijackings and "runners,'' planes that do not answer or do not heed air traffic controllers. But FAA officials would not say when controllers detected the errant Flight 77 or whether any fighter jets were able to get into the air to confront it.

Fighter jets are based nearby, in Virginia, and could have reached the White House within minutes, aviation sources say.

"Controllers at the Boston Center knew American Airlines Flight 11, which departed at 7:59 a.m. ET from Boston for its flight to Los Angeles, was hijacked 30 minutes before it crashed. They tracked it to New York on their radar scopes. 'I watched the target of American 11 the whole way down,' said Boston controller Mark Hodgkins. "

But the government claims that it could not locate the hijacked planes because the skies were crowded with other planes, and the military air traffic controllers could not find the planes among all of the plane signals. As NEADS' Thornton said:

"But the area was so congested and it was incredibly difficult to find. We were looking for little dash marks in a pile of clutter and a pile of aircraft on a two-dimensional scope.” Each fluorescent green pulsating dot on their radar scopes represents an airplane, and there are thousands currently airborne, especially over the busy northeast US.

Moreover, it makes no sense that air traffic controllers could not focus their radar scopes solely on airplanes without transponder signals. In other words, let's say a Cuban jet flew onto the East Coast of the United States without any transponder signal. Would Norad say "Sorry, we lost the bad guy's nuclear-armed fighter jet amidst all the commuter flights"?

Air traffic control radar, or at least military radar, must -- with the push of a button -- be able to use computer programming to hide all data for planes which have been accounted for as normal, civilian airplanes. In other words, those with working transponder signals. Even if air traffic controllers have to switch from secondary to primary radar, there must be a function for the computer to remove from primary radar signals which include transponder data.

If that were not the case, America's trillion-dollar defense system would be rendered useless.

I just want to add to your blog the following. The 911 official report states in The notes for Chapter 1 ref 144 "The Washington Centres controllers were looking for the flight but were not told to look for the primary" The transponder was OFF!! So what were they looking for?.

Perhaps the data feed to the ATC displays were disconnected and false data was fed in - this is not hard to do and would not involve many people. This could be why they could not find flight 77.

Most people know exactly where they were at the time of 911 including all those private planes flying in the vicinity of flight 77. They may also have a record of their own flight information, hence would expect to see their primary returns on any radar display. This data could then be compared to the ATC display observed by the controllers. If false data was fed to the ATC displays the private planes would not show up. Perhaps that is why the radar display viewed by the ATC controllers has never been released.